Aluminum bronze alloy and method having improved wear resistance



illi i ts atc time cousin No Drawing. Filed Sept. 9, 1957, Ser. No. 682,641 Claims. (Cl. 75-162) This invention relates to an aluminum bronze alloy and more particularly to an aluminum bronze alloy having improved toughness and Wear resistance.

Aluminum bronze alloys have for years been used as dies for forming and drawing operations for a large group of sheet and plate alloys such as stainless steel, aluminum, nickel, titanium, mild steel and some copper base alloys. Aluminum bronze alloy used in die applications possess the properties of good corrosion resistance, wear resistance, and non-gelling against many wrought materials.

The aluminum bronze alloys which in the past have shown the optimum properties for deep drawing dies are those that contain approximately 14% aluminum, a small amount of iron, and the balance copper. An alloy of this type has good corrosion resistance and non-galling properties. However, under heavy use in die application, it Wears undesirably fast so that close dimensional tolerances cannot be maintained because of the wear that occurs on the die surface.

The present invention is directed to an aluminum bronze alloy which has the corrosion resistance and the non-gelling properties characteristic of aluminum bronze alloys but has greatly improved wear resistance and toughness.

The aluminum bronze alloy of the invention has high uniform hardness, good toughness, excellent wear resistance and improved machinability. This is accomplished by the addition of a small amount of cobalt which renders the alloy less susceptible to eutectoid transformation and its embrittling structure, more homogeneous in the distribution of the metallurgical phases and compounds during solidification and heat treatments, and also promotes uniform controlled grain size.

The alloy of this invention has the following general composition by weight:

Percent Aluminum 13.020.0 Iron 1.0--8.0 Cobalt 0.5-5.0 Copper Balance A specific illustration of the'composition of the alloy of the invention falling within the above range is as follows in weight percent:

Percent Aluminum 16.01 Iron 5.19 Cobalt 3.68

Copper 75.12

The wear resistance of an alloy of the invention containing cobalt as compared with that of an ordinary aluminum bronze alloy is illustrated in the following table:

Wear rate in grams per 1,000 mkg. of frictional work Hardness, 0

Chemical composition Alloy Mating alloy No Cu A1 Fe 18-8 stainless steel.

Do. Do. Do.

The wear test results of the above table were obtained on a rolling-slip friction device, such as an Amsler wear test machine. In these tests the aluminum bronze alloy cylindrical test specimens were subjected to rolling and sliding motions against stainless steel cylinders with an applied compressive stress of 31,500 p.s.i. on the specimens. The test specimens 1, 2 and 3, in the table, contain only iron and aluminum in combination with copper and have a substantially lower resistance to wear than specimen number 4 which falls within the scope of the present invention. The increase in wear resistance due to the addition of cobalt to aluminum bronze is most significant since the hardness of all specimens are substantially the same.

With the cobalt addition to aluminum bronze alloys the wear rate of the alloy against stainless type steels will be less than 0.00500 gram per 1000 meter kilograms (mkg) frictional work as measured by an Amsler wear testing machine and generally in the range of 0.00300 to 0.00400 gram per 1000 meter kilograms (mkg.) of frictional work.

In addition, the alloy has a hardness in the range of 25 Rockwell C to 55 Rockwell C, depending upon the specific aluminum and cobalt contents in the alloy.

In addition to substantially increasing the wear resistance of the alloy the cobalt also makes the alloy less susceptible to the eutectoid transformation. The eutectoid structure consists of alpha phase plus gamma two phase formed from the transformation-decomposition of the beta phase. This transformation occurs at temperatures below 1050 F. in aluminum bronze alloys and the resultant eutectoid structure is brittle and possesses low ductility and poor machinability.

The alloy of the invention containing about 16% aluminum, 5% iron, and 3.5% cobalt with the balance being substantially copper can be cast either statically or centrifugally to produce a fine grained tough structure having a hardness of approximately 39 Rockwell C. This alloy displays unusual compressive strength and test specimens have registered over 200,000 p.s.i. in ultimate compression.

The metallographic structure of the above alloy consists essentially of gamma two phase which is uniformly distributed in a matrix of beta. An intermetallic compound composed of iron, aluminum, copper and cobalt exists in rosette shaped particles. Because of the method of casting and the inoculant used, the intermetallic compound is uniformly distributed throughout the cast section.

In order to obtain optimum properties, the metals used for the alloy should be of high quality. Electrolytic or wrought fire refined copper, high purity aluminum, low carbon iron, and high purity cobalt are preferred to be used. It has also been found that the best method of obtaining the desired uniformity in the alloy is by using a double melting procedure whereby a pre-alloy is made. The most satisfactory pro-alloy is one that has approximately 50% aluminum, 20% copper, 20% iron and 10% cobalt.

The melting procedure employed in making the prealloy is such that some copper, along with the iron and cobalt, is placed into the crucible and melting begun. When the copper starts to melt, the iron and other additives are slowly dissolved into the copper during that period when aluminum is added to form an exothermic reaction which helps to dissolve the higher melting point cobalt addition. This pre-alloy is then cast into ingot form and is ready to use for the final alloy.

The final alloy is made by intermixing a predetermined percentage of the pre-alloy and copper. A deoxidizer is added to this alloy in the molten state in the furnace to purge the metal of oxides and soluble gases.

These deoxidizers can include the compounds of boron, phosphorus, manganese, magnesium, and lithium. Deoxidizers of the gas type can also be used. This can include volatile chlorides or any of the inert gases. The dry type deoxidizers are addded in quantities of approximately 4 ounces per 100 pounds of metal, and the gas type deoxidizers are passed either through or over the molten metal for a period of five minutes. Removal of the oxide particles is of particular importance because of their abrasive and adverse efiect on the wear-resistant properties of the alloy.

To establish complete uniformity of the microstructure and hardness the alloy is heat treated at an elevated temperature in the temperature range of 1050 F. to 1400 R, such as about 1150 F. Small castings of simple shapes of this alloy can be placed directly into the heat treating furnace at temperature. Large massive castings or intricate shapes are preheated in the furnace at about 400 F. until the section reaches uniform temperature and then are heated directly to the elevated temperature. The castings are held at a temperature in the range of 1050" F. to 1400" F. for one hour plus one-half hour per inch of section thickness greater than one inch, up to a maximum of two and one-half hours at temperature.

After the required soaking time at the elevated temperature, the alloy is cooled at a rate faster than about 20 F. per hour per one inch of section thickness. This rate is conveniently obtained by fan air cooling.

Internal stresses created within castings during machining or other finishing operations, during weldments or from metal overlays on base metals, are usually removed depending on the future application of the part. These stresses are removed by a stress relief heat treatment. The usual commercial aluminum bronze alloys cannot generally be stress relieved at a temperature in the range of 650 F. to 1050 F. due to eutectoid formation that occurs at this temperature range. Furthermore, a stress relief at temperatures above 1050 F. frequently causes distortions and further stresses in the usual commercial aluminum bronze alloy during the rapid cooling to room temperature. Stress relief at temperatures lower than 650 F. takes considerable time and often the most severe stresses remain.

In contrast to this, the alloy of the invention can be stress relieved within the temperature range of 650 F. to 1050 F. without embrittlernent due to the excessive eutectoid structure. An optimum stress relief tempera ture for the present alloy, based on the severity of the internal stresses and geometry of the article, can be selected in the range of 650 F. to 1050" F. to obtain a reasonable holding time in the furnace, such as one to two hours per 2 inches of section, and to prevent distortions and micro stresses during cooling. The article is then cooled to room temperature.

Small amounts of metals, such as tin, zinc, lead, nickel, silicon and beryllium can be present in the alloy up to about 1% by weight without adversely affecting the characteristics of the present alloy.

The alloy of this invention can be used to produce articles that require corrosion resistance, toughness, and exceptional wearing properties. The articles may take the form of deep drawing dies, Wear guides, forming rolls, etc.

The alloy can also be extruded into weldrods or weld Wire. The alloy in the form of coated or uncoated weldrod can be overlaid on a base metal by metal spraying or other welding methods, such as heli-arc, metal-arc, carbon-arc, etc. to obtain a corrosion resistant wear surface. The metal overlay can be given a stress relief treatment at temperatures in the range of 650 F. to 1150 F. and cooled to room temperature.

It has been found that the addition of cobalt to the copper-aluminum-iron alloys to be used as die materials greatly improves the toughness and wear resistance of the alloy and makes it less susceptible to eutectoid embrittlement.

In addition, the alloy of the invention has not only increased toughness, strength, and wear resistance but also has improved machinability by controlling the distribution of the various component phases. The improved machinability permits die sinking of more intricate designs on die surfaces than was previously possible on ordinary aluminum bronze die alloys.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. An aluminum bronze alloy, consisting essentially of 13% to 20% aluminum, from 1% to 8% iron, from 0.5% to 5% cobalt, and the balance being substantially copper, said alloy being characterized by having excellent corrosion resistance and having improved toughness and wear resistance.

2. An aluminum bronze alloy consisting essentially of from 13% to 20% aluminum, from 1% to 8% iron, from 0.5% to 5% cobalt, and the balance being substantially copper, the said alloy having a wear rate of less than 0.005 grams per 1000 meter kilograms of frictional Work as measured on a rolling-slip wear testing machine.

3. An aluminum bronze alloy consisting essentially of from 13% to 20% aluminum, from 1% to 8% iron, from 0.5% to 5% cobalt, and the balance being substantially copper, said alloy having a Wear rate of less than 0.005 grams per 1000 meter kilograms of frictional Work as measured on a rolling-slip wear testing machine and having a hardness in the range of 25 to 55 Rockwell C.

4. An aluminum bronze alloy having improved toughness and Wear resistance consisting essentially of 16.01% aluminum, 5.19% iron, 3.68% cobalt, and 75.12% copper.

5. A die for deep drawing sheet and plate alloys and having a forming surface fabricated from an aluminum bronze alloy having improved toughness and wear resistance, said aluminum bronze alloy consisting essentially of 13% to 20% aluminum, from 1% to 8% iron, from 0.5% to 5% cobalt, and the balance being substantially copper, said alloy having improved homogeneity of structure and uniformity of hardness by heating the alloy to a temperature of 1150 F. and thereafter cooling at a rate faster than 20 F. per hour per one inch of section thickness to room temperature.

6. A die for forming sheet and plate alloys and having a forming surface fabricated from an aluminum bronze alloy characterized by having excellent corrosion resistance, a hardness in the range of 25 to 55 Rockwell C and a Wear rate of less than 0.005 grams per 1000 meter kilograms of frictional work as measured by a rollingslip wear testing machine, said aluminum bronze alloy consisting essentially of 13% to 20% aluminum, from 1% to 8% iron, from 0.5% to 5% cobalt, and the balance being substantially copper.

7. An aluminum bronze welding electrode consisting essentially of 13% to 20% aluminum, from 1% to 8% iron, from 0.5% to 5% cobalt, and the balance being substantially copper.

8. A method of heat treating an aluminum bronze alloy consisting essentially of 13% to 20% aluminum, 1% to 8% iron, 0.5% to 5% cobalt and the balance copper to establish uniformity of the microstructure and hardness in the alloy, comprising heating the alloy to a temperature in the range of 1050 F. to 1400 F., retaining said alloy at said temperature for a period of one hour plus one-half hour per inch of section thickness greater than one inch up to a maximum period of two and one-half hours, and cooling the alloy from said temperature at a rate faster than 20 F. per hour per one inch of section thickness to room temperature.

9. A method of heat treating an aluminum bronze alloy consisting essentially of 13% to 20% aluminum, 1% to 8% iron, 0.5% to 5% cobalt and the balance copper to establish uniformity of the microstructure and hardness in the alloy, comprising heating the alloy to a temperature in the range of 1050 F. to 1400 F., retaining said alloy at said temperature for a period of one hour plus one-half hour per inch of section thickness greater than one inch up to a maximum period of tWo and one-half hours, cooling the alloy from said temperature at a rate faster than 20 F. per hour per one inch of section thickness to room temperature, heating the alloy to a temperature in the range of 650 F. to 1050 F., and thereafter cooling the alloy to room temperature.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Aluminum Bronze, issued by the Copper Development Assoc. (London), N0. 31, (1939), pp. 68, 69. 

1. AN ALUMINUM BRONZE ALLOY CONSISTING ESSENTIALLY OF 13% TO 20% ALUMINUM, FROM 1% TO 8% IRON, FROM 0.5% TO 5% COBALT, AND THE BALANCE BEING SUBSTANTIALLY COPPER; SAID ALLOY BEING CHARACTERIZED BY HAVING EXCELLENT CORROSION RESISTANCE AND HAVING IMPROVED TOUGHNESS AND WEAR RESISTANCE 